The search for new therapeutic agents has been greatly aided in recent years by better understanding of the structure of proteins and other biomolecules associated with target diseases. One important class of these proteins is the sigma (σ) receptor, a cell surface receptor of the central nervous system (CNS) which may be related to the dysphoric, hallucinogenic and cardiac stimulant effects of opioids. From studies of the biology and function of sigma receptors, evidence has been presented that sigma receptor ligands may be useful in the treatment of psychosis and movement disorders such as dystonia and tardive dyskinesia, and motor disturbances associated with Huntington's chorea or Tourette's syndrome and in Parkinson's disease (Walker, J. M. et al, Pharmacological Reviews, 1990, 42, 355). It has been reported that the known sigma receptor ligand rimazole clinically shows effects in the treatment of psychosis (Snyder, S. H., Largent, B. L. J. Neuropsychiatry 1989, 1, 7). The sigma binding sites have preferential affinity for the dextrorotatory isomers of certain opiate benzomorphans, such as (+)SKF 10047, (+)cyclazocine, and (+)pentazocine and also for some narcoleptics such as haloperidol.
The sigma receptor has at least two subtypes, which may be discriminated by stereoselective isomers of these pharmacoactive drugs. SKF 10047 has nanomolar affinity for the sigma 1 (σ-1) site, and has micromolar affinity for the sigma 2 (σ-2) site. Haloperidol has similar affinities for both subtypes. Endogenous sigma ligands are not known, although progesterone has been suggested to be one of them. Possible sigma-site-mediated drug effects include modulation of glutamate receptor function, neurotransmitter response, neuroprotection, behavior, and cognition (Quirion, R. et al. Trends Pharmacol. Sci., 1992, 13:85-86). Most studies have implied that sigma binding sites (receptors) are plasmalemmal elements of the signal transduction cascade. Drugs reported to be selective sigma ligands have been evaluated as antipsychotics (Hanner, M. et al. Proc. Natl. Acad. Sci., 1996, 93:8072-8077). The existence of sigma receptors in the CNS, immune and endocrine systems have suggested a likelihood that it may serve as link between the three systems.
In view of the potential therapeutic applications of agonists or antagonists of the sigma receptor, a great effort has been directed to find selective ligands. Thus, the prior art discloses different sigma receptor ligands. 4-[2-[[5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]morpholine is one of such promising sigma receptor ligands. The compound and its synthesis are disclosed and claimed in WO2006/021462.
4-[2-[([5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]morpholine is a highly selective sigma-1 (σ-1) receptor antagonist. It has displayed strong analgesic activity in the treatment and prevention of chronic and acute pain, and particularly, neuropathic pain. The compound has a molecular weight 337.42 uma. The structural formula of the compound is:

The solid state physical properties of a pharmaceutical compound can be influenced by the conditions under which the compound is obtained in solid form. Solid state physical properties include, for example, the flowability of the milled solid which affects the ease with which the compound is handled during processing into a pharmaceutical product. Another important solid state property of a pharmaceutical compound is its rate of dissolution in aqueous fluid. The rate of dissolution of an active ingredient in a patient's stomach fluid can have therapeutic consequences because it imposes an upper limit on the rate at which an orally administered active ingredient can reach the blood. The solid-state form of a compound may also affect its solubility, bioavailability, behavior on compaction, stability, or its electrostatic nature.
Polymorphism is the property of some molecules and molecular complexes to assume more than one crystalline or amorphous form in the solid state. In general, polymorphism is caused by the ability of the molecule of a substance to change its conformation or to form different inter molecular and intramolecular interactions, particularly hydrogen bonds, which is reflected in different atom arrangements in the crystal lattices of different polymorphs. Accordingly, polymorphs are distinct solids sharing the same molecular Formula, having distinct advantageous and/or disadvantageous physical properties compared to other forms in the polymorph family.
The term “solvate” refers to any solid form of a given compound in which said compound is bonded by a non-covalent bond to molecule(s) of solvent (normally a polar solvent).
The discovery of new crystalline polymorphic or amorphous forms of a pharmaceutical compound provides an opportunity to improve the physical or performance characteristics of a pharmaceutical product in that it enlarges the repertoire of materials that a formulation scientist has available for designing, for example, a pharmaceutical dosage form of a drug with a targeted release profile or other desired characteristics.
Therefore, there is still a need in the art for additional forms of 4-[2-[[5-methyl-1-(2-naphthalenyl)-1H-pyrazol-3-yl]oxy]ethyl]morpholine to carry out its pharmaceutical development and release its potential, and facilitate the preparation of better formulations of this active pharmaceutical ingredient. In this regard, different morphological forms of the compound may have widely different properties such as, for example, enhanced thermodynamic stability, higher purity or improved bioavailability (e.g. better absorption, dissolution patterns) and could either become intermediates for other forms or provide in themselves a still better formulation of this active pharmaceutical ingredient. Specific compound forms could also facilitate the manufacturing (e.g. enhanced flowability), handling and storage (e.g. non-hygroscopic, long shelf life) of the compound formulations or allow the use of a lower dose of the therapeutic agent, thus decreasing its potential side effects. Thus it is important to find such forms, having desirable properties for pharmaceutical use.